Abstract Title: SST North American Drought Links in 20th Century Simulations and 21st Century Climate Projections

Abstract: The present work assesses the SST structure of some CMIP3 (IPCC AR4) climate models associated with low-frequency summer rainfall variability over central US. To facilitate examination of the model simulations and projections, a seasonal precipitation-based drought index is devised to capture low-frequency hydroclimate variability; it is built applying twelve times a 1-2-1 binomial filter to seasonal precipitation anomalies averaged over the Great Plains. The devised index is correlated at ~ 0.8 with the Palmer Drought Severity Index over the Great Plains. A similar index is created for simulations of the 20th century climate, and the projections under the A1B scenario. Observations indicate that summer low-frequency precipitation variability during the 20th century is associated with SST anomalies over both the Pacific and Atlantic Oceans; positive/negative SST anomalies over the Pacific/Atlantic Ocean favor drought conditions over central US. Summer low-frequency precipitation variability during the 20th century in models also exhibits a connection with SST anomalies over both oceans; although the SST structure in models is not identical to that in observations, the sign of the anomalies (positive/negative Pacific/Atlantic) is reasonably simulated. The increase of CO2 during the 21st century in the A1B scenario alters the low-frequency variability of precipitation over central US; the models tend to produce more multi-year droughts over the region with a different SST structure to that simulated in the 20th century.